The present invention relates to a velocity error signal generation method and the apparatus thereof, and, more particularly, to a method and apparatus for generating accurate velocity error signals, by replacing an undesired actual velocity with a command velocity when the undesired actual velocity is generated due to external noise or unexpected disturbances, in controlling a track traverse velocity for a magneto-optical disk drive.
Generally, in the field of control technology, when controlling the velocities of objects, a velocity error corresponds to the difference between a desired command velocity and an actual velocity generated in response to the command velocity, which is thereby used in the control of the object's velocity. That is, by subtracting the actual velocity from the command velocity, the obtained velocity error is used in a velocity control operation.
In most cases, accurate velocity errors can be obtained, but when the actual velocity is not accurately measured due to noise or other causes, incorrect velocity error signals are generated. When such an incorrect velocity error signal is directly used as a velocity control signal, accurate velocity control cannot be achieved.
FIG. 1 shows a schematic block diagram of the conventional velocity error generation apparatus. Signals from an actual velocity generator 10 and a command velocity generator 11 are input to a velocity error generation apparatus 12, which generates a velocity error signal by subtracting the actual velocity from the command velocity.
However, when the actual velocity error includes noise, an incorrect velocity signal is generated.
FIGS. 2A, 2B and 2C are waveform diagrams showing operations of the conventional velocity error generator with respect to an actual velocity signal which includes noise.
As shown in FIG. 2B wherein actual velocity voltage is shown, an incorrect signal 20 due to noise is included in a waveform of the actual velocity voltage signal. In this case, such a signal 20 due to the noise appears unchanged in a velocity error voltage signal (which is obtained by subtracting an actual velocity voltage as shown in FIG. 2B from a command velocity voltage as shown in FIG. 2A).
For example, the magneto-optical disk drive utilizes a light beam to find a user-desired target track with a track detection signal of an optical head which detects a precise information signal stored on a disk surface. Accordingly, the track detection signal can be incorrectly generated by defects in the disk surface, an offset detection flag region and a preformat region, by the sway of a portable magneto-optical disk drive, etc. As a result, incorrect velocity error signals are generated.
Thus, if velocity control is performed according to such an incorrect velocity error signal, the actual velocity deviates from a minute voltage difference range of a command velocity to be controlled, that is, a normal state range, to thereby make correct velocity control impossible. Accordingly, as an incorrect actual velocity is generated due to noise or unexpected disturbance, a velocity error generator which generates a correct velocity error signal is necessary.